A visible-light photoinduced charge-transfer complex promoted the ring opening of: N-alkyl-4-piperidinols

Article abstract of DOI:10.1039/d0gc00196a

A visible-light photoinduced ring opening of N-alkyl-4-piperidinols under mild conditions has been achieved. The reaction sequence involves a visible-light-induced charge-transfer complex, which promoted the S-Cl bond cleavage of sulfonyl chlorides. The generated sulfonyl radical further reacts with N-alkyl-4-piperidinol cation radicals to achieve C-N and C-C bond cleavages to yield homoallylamine products.

Full text of DOI:10.1039/d0gc00196a

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DOI: 10.1039/D0GC00196A
COMMUNICATION
Ying Fu, Chun–Zhao Shi, Qin–Shan Xu,
OH
Visible light promotion
CT-complex activation
Remote OH group assistance
Regiospecific E alkenes formation
C-N & C-C bond cleavages
R
R
Zhengyin Du and Congde Huo
TsCl
, alizarin yellow R
Ts
MeCN, white LED lamp
N
Visible-Light Photoinduced
Charge-Transfer Complex Promoted
the Ring Opening of
N
R'
R'
(E)-homoallylamines are efficiently prepared through visible-light photoinduced
N-Alkyl-4-Piperidinols
charge-transfer complex promoted ring-opening of N-alkyl-4-piperidinols.

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DOI: 10.1039/D0GC00196A
ARTICLE
Visible-Light Photoinduced Charge-Transfer Complex Promoted
the Ring Opening of N-Alkyl-4-Piperidinols
Ying Fu,* Chun-Zhao Shi, Qin-Shan Xu, Zhengyin Du* and Congde Huo*
Received 00th January 20xx,
Accepted 00th January 20xx
A visible-light photoinduced ring opening of N-alkyl-4-piperidinols under mild conditions has been achieved. The reaction
sequence involves a visible-light-induced, charge-transfer complex, which promoted S–Cl bond cleavage of sulfonyl
chlorides. The generated sulfonyl radical further reacts with N-alkyl-4-piperidinol cation radicals to achieve C–N and C–C
bond cleavages to yield homoallylamine products.
DOI: 10.1039/x0xx00000x
a) Oxidative ring-opening via C-N bond cleavage
O
Introduction
Ru Porphyrin
BzNH
OH
N
The ubiquity of carbon–nitrogen bonds in organic compounds
has promoted the continuous development of the formation
and transformation of C-N bonds in organic chemistry.[1] Over
the past decades, considerable efforts have been devoted to
the development of methods for C–N bond functionalization.[2]
Among them, the activation and further transformation of C–N
bonds in unstrained saturated aliphatic cyclic amines is
particularly intriguing given that C–N bond dissociation and ring
opening provide carbon and nitrogen terminals for
modification, resulting in a scaffold that is more structurally
diverse than that of acyclic amines. However, the efficient
accomplishment of this purpose remains limited due to high C–
N bond dissociation energy.[3] Several strategies for ring-
opening functionalization of unstrained cyclic amines have been
developed, which are dominated by α-oxidation followed by
heterolytic C–N bond cleavage (Scheme 1(a)).[4] The destructive
functionalization of cyclic amines has received special attention
because of unusual carbon–carbon bond cleavage. In this
scenario, Roque et al. found that saturated unstrained cyclic
amines, such as piperidines and pyrrolidines, could be
converted into halogen-containing acyclic amine derivatives
through C(sp3)–C(sp3) and/or C(sp3)–N bond cleavage followed
by C(sp3)–halogen bond formation (Scheme 1(b) and (c)).[5]
Light has now been recognized as an ideal source of energy
because of its abundance and environmental friendliness. The
dramatic evolution of visible light photoredox catalysis[6]
2,6-Dichloropyridine N-Oxide
(ref. 4e)
Bz
b) Oxidative ring-opening via C-C bond cleavage
F
AgBF4 (4 equiv)
Selectfluor
(4 equiv)
N
(ref. 5a)
N
O
Acetone:H2O (1:9)
40 °C, 1h
Bz
Bz
c) Oxidative ring-opening via C-C and C-N bonds cleavages
AgNO3 (4 equiv.)
Cl/Br
(NH4)2S2O8 (4 equiv.)
NCS or NBS
NH
Piv
N
(ref. 5b)
Acetone:H2O (1:9)
RT, 30 min.
Piv
d) This work: visible light induced, 4-OH assisted C-C and C-N bond cleavages
OH
Visible light promotion
CT-complex activation
Remote OH group assistance
Regiospecific E alkenes formation
C-N & C-C bond cleavages
R
R
TsCl, alizarin yellow R
Ts
MeCN, white LED lamp
N
N
R'
R'
Scheme 1. Strategies for intra-annular C–N and C–C bond
cleavages and functionalization
yields or selectivity, can now be accessed in a mild, efficient, and
selective manner. This burgeoning technology has been utilized
to activate and further modulate, in most cases, the alpha C–H
bond of amines rather than the C–N bond.[7] Hitherto, only a few
photoinduced C–N bond dissociation protocols have been
developed, and only a few reactive amine species, e.g.,
diazonium salts,[8] alkyl Katritzky salts,[9] and arylhydrazines,[10]
are effective substrates.
Charge-transfer complexes (CT complexes), or electron
donor–acceptor complexes formed via the partial transfer of
electrons from the electron donors to the electron acceptors,
have gained considerable attention in many fields of
chemistry.[11] Synthetically, the formation of CT complexes can
significantly attenuate the electronic density around the donor
atom and thus activates the chemical bonds to which the donor
atom participates. Previously, we reported an interesting C–N
promises that numerous single electron-transfer reactions,
previously performed under harsh conditions or afforded low
College of Chemistry & Chemical Engineering, Northwest Normal University
East Road 967, An’ning, Lanzhou, China
E-mail: fu_yingmail@126.com; zhengyin_du@nwnu.edu.cn;
huocongde@nwnu.edu.cn.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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bond cleavage of tertiary ethylene-1,2-diamines[12] in the photocatalyst, and a 30 W white LED as the light VsioewurAcrteicleuOnndliener
DOI: 10.1039/D0GC00196A
presence of sulfonyl chlorides, whereby the ethylenic C–N room temperature conditions for 24 h.
bonds are activated by a CT complex that formed in situ
Table 1. Optimization of the reaction conditions[a]
between the two reactants. Furthermore, one ethylenic C–N
Me
1a
TsCl ( ), photocatalyst
bond was regiospecifically cleaved with the help of another
nitrogen atom. Inspired by this finding, we thus hypothesized
that one intra-annular C–N bond of N-alkyl-4-piperidinol,[13, 14]
in the presence of sulfonyl chlorides, might also perform a
similar reaction given that a CT complex can also be formed
between the two reactants, namely, sulfonyl chloride and N-
alkyl-4-piperidinol. Furthermore, the remote hydroxyl group in
piperidinol might play a role in C–N bond dissociation. In
addition, because almost all CT complexes have unique and
intense absorption bands in the ultraviolet–visible (UV–Vis)
region, we speculated that visible light might play a role in
activating the inert C(sp3)–N bonds of unstrained N-alkyl-4-
piperidinols.
N
HO
N Me
Ts
CaH2, white LED, N2
3a
2a
Entry
Solvent
Photocatalyst (mol%)
Yield [%][b]
1
2
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
CH2Cl2
CHCl3
Toluene
THF
[Ru(bpy)3]Cl2·6H2O (5)
Rose bengal (5)
Eosin Y (5)
0
0
3
51
0
4
Solvent Red 49 (5)
Alizarin yellow R (5)
Alizarin yellow R (2)
Alizarin yellow R (2)
Alizarin yellow R (2)
Alizarin yellow R (2)
Alizarin yellow R (2)
Alizarin yellow R (2)
－
5
77
75
45
60
57
53
48
trace
6
7
8
9
10
11[c]
12[d]
Results and discussion
MeCN
MeCN
We performed our studies on the coupling of TsCl 1a with N-
methyl-4-piperidinol (NMP) 2a using [Ru(bpy)3]Cl2·6H2O (0.05
equiv.) as the photoredox catalyst under irradiation with a 30 W
white LED lamp. However, no reaction occurred (Table 1, entry
1). Dyes have been proven as environmentally friendly,
inexpensive, and easy-to-handle photoredox catalysts that
promote a large variety of organic reactions, and some organic
dyes are particularly attractive because their redox properties
remarkably resemble those of metal complexes.[15] Thus, Rose
Bengal was first screened, and it failed to promote coupling
(entry 2). When Eosin Y was adopted as the organocatalyst, a
homoallylamine product 3a, formed via C–N and C–C bond
cleavages of N-methyl-4-piperidinol 2a, was formed (entry 3).
Further investigations showed that alizarin yellow R (AYR) was
the most efficient organocatalyst, and 77% isolated yield of 3a
was obtained (entries 4–6). Moreover, the reaction of 1a
proceeded with the same high efficiency and selectivity even
when a stoichiometric amount of 2a (1.2 eq.) and reduced AYR
loading (2.0 mmol%) were used (entry 6, optimal condition).
Subsequently, several solvents were screened, and acetonitrile
was identified as the optimal solvent because the photocatalyst
AYR was fully dissolved in acetonitrile (entries 7–10). Finally,
comparative experiments were conducted, which illustrated
that the photocatalyst and the light source were important for
the reaction (Table 1, entries 11–12). Notably, CaH2 (40 mg, 1.0
mmol) was shown to play a key role in the reaction
transformation by quickly removing trace amounts of moisture
in the reaction system, in addition to neutralizing the HCl by-
product, to prevent the hydrolysis of sulfonyl chlorides.
However, removing all moisture from the reaction system is
impossible because piperidinols and sulfonyl chlorides are
hygroscopic materials.[16] In summary, the optimal reaction
system was identified to comprise TsCl and N-methyl-4-
piperidinol as the reaction substrates, AYR (2 mol%) as the
[a] Reaction conditions: TsCl (1a, 1.0 mmol), N-methy-4-piperidinol (2a,
1.2 mmol), photocatalyst, CaH2 (40 mg), 30 W white LED, rt, N2, 24h.
[b]. Isolated yields. [c] Blue LED. [d] Without LED.
Having identified these optimal conditions and catalysts, we
tested the reactivity of N-methyl-4-piperidinol 2a (Table 2).
Various substituted arylsulfonyl chlorides provided the desired
homoallylamine products in moderate to high yields (Table 2).
Arylsulfonyl chlorides fixed with electron-donating groups,
including alkyl (products 3a and 3b) and OCF3 (products 3f and
3g), and electron-withdrawing groups, such as CF3 (products 3c–
3e), Br (product 3i), F (products 3j & 3k), and NO2 (product 3l),
on the phenyl rings reacted smoothly with 2a to produce the
desired homoallylamine products in high yields under our
photocatalytic system. The highly sterically constrained 2,4,6-
triisopropylbenzenesulfonyl chloride could perform such
transformation and delivered the desired product 3b with 63%
yield, demonstrating the wide applicability of this reaction
protocol. Furthermore, polycyclic and heterocyclic aryl sulfonyl
chlorides (products 3m–3p) were compatible with this reaction.
Notably, aliphatic sulfonyl chlorides were unsuitable substrates
for this reaction system, and the desired products were not
formed.[17]
Next, the scope of substituents that could be appended to 4-
piperidinols in this photoinduced C–N and C–C bond cleavage
protocol was investigated (Table 3). N-ethyl and N-propyl
homoallylamines were successfully prepared from the
corresponding N-ethyl and N-propyl 4-piperidinols with 56% to
86% isolated yields (products 4a–4f). When 2-
nitrobenzenesulfonyl chloride was utilized as the reactant, a
slightly low yield of 4f was obtained partially due to the
instability of 2-nitrobenzesulfonyl chlorides under this reaction
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
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condition. Interestingly, when N,3-dimethyl-4-piperidinol was This approach provided the terminal alkene 12 inV7ie3w%ArtiiscloelOantleinde
DOI: 10.1039/D0GC00196A
used, only (E)-homoallylamines 4i–4m were obtained,
Table 2. Substrate scope of sulfonyl chlorides[a,b]
yield.
Table 3. Substrate scope of N-alkyl 4-piperidinols[a,b]
R2
Me
1
RSO2Cl ( ), AYR, CaH2
O O
S
N
1
ArSO2Cl ( ), AYR, CaH2
HO
N Me
RO2S
N
R1
R2
HO
CH3
CH3
MeCN, white LED, N2
Ar
N
MeCN, white LED, N2
3
2a
R1
2
4
O
S
O
O
O
O
O
S
N
Me
S
N
Cl
S
N
S
N
S
N
CH3
N
Me
O
O
O
Me
O
O
O
CF3
3c,
4a,
78%
3a,
71%
75%
3b,
4b, 86%
4c,
63%
80%
NO2
O
S
O
S
O
S
O
S
O
S
O
Cl
F3C
N
F3C
N
N
N
N
S
N
Me
Me
Me
O
O
O
O
O
O
OCF3
3d,
77%
3e,
81%
3f,
73%
4f,
4d,
4e,
56%
80%
77%
O
S
O
O
O
S
O
F3CO
N
Me
Br
S
N
Me
S
N
Me
O
S
CH3
N
S
N
O
O
O
CH3
N
O
O
CH3
O
3h,
70%
3g,
80%
3i,
N
76%
F
F
4g,
83%
4h,
77%
4i,
76%
O
S
O
S
O
F
N
Me
N
Me
N
Me
O2N
S
Cl
O
O
O
O
S
O
S
O
S
F
N
CH3
3j,
63%
F
N
CH3
F3C
N
3k,
74%
3l,
66%
O
CH3
O
O
F
S
4k
, 61%
4j
, 84%
4l,
O
70%
O
S
O
O
S
S
OEt
N
Me
S
N
Me
N
Me
O
O
O
O
S
O
S
O
S
N
3o,
76%
3m,
83%
3n,
79%
CH3
N
N
CH3
N
Ph
Ph
CH3
78%
O
O
O
O
H3CO
O
S
O
S
O
4m,
4o,
79%
4n
, 68%
N
Me
S
CH3
N
Me
S
N
Me
O
O
O
3p,
3q,
64%
0%
3r,
64%
[a] Reaction conditions: 1 (1.0 mmol), 2 (1.2 equiv), AYR (2 mol%), CaH2 (40
mg), 30 W white LED, rt, 24 h. [b] Isolated yields.
[a] Reaction conditions: 1 (1.0 mmol), 2a (1.2 mmol), AYR (2 mol%), CaH2 (40
mg), 30 W white LED, rt, N2, 24 h. [b] Isolated yields.
1a
TsCl ( ), alizarin yellow R
(a)
(b)
HO
N
N
Bn
HO
HO
N Ts
demonstrating the stereospecificity and regiospecificity of this
ring-opening protocol. Notably, N-cyclopropyl and N-(2-
phenylethyl) 4-piperidinols (4h and 4n) also participated in the
desired coupling reactions without the loss of efficiency or
MeCN, 30W white LED
6
(67%)
5
HO
TsCl (1a), alizarin yellow R
Bn
N
Ts
MeCN, 30W white LED
8
(70%)
Ts
7
selectivity. 2-Thienylsulfonyl chloride,
a
representative
1a
TsCl ( ), alizarin yellow R
heteroaryl sulfonyl chloride, participated in this transformation
well and gave the desired homoallylamine product 4o in 78%
isolated yield.
(c)
(d)
HO
N Me
HO
N
MeCN, 30W white LED
9
10
(58%)
1a
TsCl ( ), alizarin yellow R
Ph
HO
Ph
O
N Ts
N Me
To further investigate the scope of substituents on N-alkyl-4-
piperidinols, several control reactions were then conducted
(Scheme 2). First, when N-benzyl-4-piperidinol 5 and N-benzyl-
3-pyrrolidinol 7 instead of 2a were reacted with TsCl 1a, the N-
debenzylated sulfonamides 6 and 8 were obtained as the main
products[18] (Scheme 2(a and b)). Unexpectedly, when 8-methyl-
8-azabicyclo[3.2.1]octan-3-ol 9 was introduced to react with
TsCl under the optimized conditions, N-demethylated
sulfonamide 10 was obtained, possibly because of the high
steric constraints around the nitrogen atom that hindered the
effect of the 4–OH group (Scheme 2(c)). As shown in Table 3,
the reactions of the 3-branched N-alkyl-4-piperidinols with
sulfonyl chlorides always yielded E-homoallylamine products
(4i–4o). Thus the 4-substituted piperidinol 11 was introduced.
MeCN, 30W white LED
11
12
(73%)
Et3N, alizarin yellow R
MeCN, 30W white LED
TsCl
CH3
S O
CH3
(e)
(f)
1a
13
(24h, 14%)
Ts
1a
TsCl ( ), alizarin yellow R
HO
N Me
N
Me
additive (2 equiv), 30W white LED
3a
2a
additive: TEMPO, 12%
BHT, 17%
OH
N+
15
N
OTs
OH
14
Calcd. 312.16279
Found: 312.16312
Calcd. 146.11756
Found: 146.11769
Scheme 2. Some control experiments.
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DOI: 10.1039/D0GC00196A
Mechanistically, these reactions may be performed via the
radical pathway, and the generation of trace amount of
sulfinates was observed through the radical decomposition of
corresponding sulfonyl chlorides during the reaction. This
postulation was assured by the control reaction listed in
Scheme 2(e) wherein TsCl alone was stable under white LED
irradiation but was gradually decomposed into p-tolyl 4-
methylbenzenesulfinate 13 (14%) in the presence of a tertiary
amine, such as, triethylamine, demonstrating the key role of the
in situ formation of a CT complex via a tertiary amine and
sulfonyl chloride that facilitated S–Cl bond cleavage. The UV–Vis
spectroscopic measurements of the combinations of 1a and 2a
in MeCN showed that when 1a and 2a were mixed in MeCN, the
color of the solution changed from colorless to yellow, and two
new absorption bands with maximum wavelengths at 320 and
408 nm appeared (Figure 1), demonstrating the formation of
the CT complex between 1a and 2a that facilitates S–Cl bond
cleavage in TsCl.[19] Notably, the UV–Vis analysis of AYR in MeCN
showed that an absorption band centered at 405 nm
appeared,[20] implying the easy transference of photo energy
between the CT complex and the existence of a photocatalyst
that might further push the reaction forward. Moreover, when
two equivalents of 2,2,6,6-tetramethylpiperidinooxy (TEMPO)
or 2,6-di-tert-butyl-4-methylphenol as a radical scavenger was
added to the standard reaction systems for the synthesis of 3a,
the formation of 3a was suppressed to less than 20% isolated
yield. The existence of radical adducts 14 in TEMPO involved in
the reaction system strongly suggested the generation of the p-
tolylsulfonyl radical intermediate. Furthermore, the capture of
N,O-acetal 15 in the reaction system indicates that
formaldehyde might be formed in the reaction (Scheme 2(f)).
1a
2a
1a+2a
Figure 1. Photos of 1a (TsCl), N-methyl-4-piperidinol (2a), and 1a+2a in MeCN
(0.2 mM) and UV-Vis absorption spectra of 1a (0.2 mM), 2a (0.2 mM), and their
mixtures (1a+2a, 0.2 mM) in MeCN.
O-
N+
O
Ts
H
N
MeCN
H
TsCl + NMP +
1a 2a
A
radical
g = 2.0058
AN = 14.57G
AH = 20.17G
333
335
337
Magnetic field (mT)
339
341
Figure 2. Experimental EPR spectrum of the reaction of 1a, 2a and DMPO in
MeCN under visible light promotion.
Electron spin resonance studies were next performed (Figure 2)
to further probe the nature of the radical species formed during
the reaction. 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) was
introduced as a spin-trap because it reacts with short-living
radicals to furnish stable and EPR-detectable nitroxide
radicals.[21] Based on previous studies,[22] radical A generated by
the reaction of TsCl 1a with NMP 2a and DMPO in MeCN was
identified as a nitroxide radical as shown in Figure 2. The
reaction of 1a leads to a DMPO-trapped radical species
featuring a triplet or doublet EPR signal due to coupling with
adjacent nitrogen and hydrogen atoms highlighted in red,
showing a g value of 2.0058. Together, these results confirmed
that under visible light promotion in the presence of NMP and
under irradiation with visible light, TsCl was decomposed to
generate a p-tolylsulfonyl radical.
A plausible mechanism for the formation of 4i was proposed
(Scheme 3) on the basis of the above experimental results.
Upon irradiation with visible light, AYR was excited and
reductively quenched by 3,N-dimethyl-4-piperidinol (2e) to
AYRˑ-, delivering a nitrogen-centered radical cation (I).[23] The
reduced catalyst (AYRˑ-) was then oxidized by visible light-
excited TsCl···2e CT complex into its normal state.
Concomitantly, a sulfonyl free radical (Ts·) was generated and
cross-coupled with the radical cation (I) to yield the carbon
cation (II), which produced an unstable trans-2,3-disubstituted
oxetanium intermediate (III) after intramolecular nucleophilic
attack of the hydroxy group. The existence of the oxetanium
intermediate in the reaction system was verified by HRMS
analysis. Finally, the pyrolysis of (III)[24] readily occurred, and the
(E)-homoallylamine product (4i), together with the
formaldehyde byproduct, was generated. Notably, due to the
high steric hindrance between the two substituents on oxetane
ring, cis-2,3-disubstituted oxetanium intermediate (IV)
might not be formed at all given that the (Z)-homoallylamine
product V was not detected by the crude 1H NMR analysis of the
reaction mixture. Nevertheless, the detection of another
homoallylamine isomer VIII (less than 10% based on 4i)
indicated that a high regioselective C–N bond cleavage of
intermediate I preferentially occurred at the C2–N bond rather
than at the C6–N bond. This regioselectivity might be ascribed
to the lower inner energy of internal alkenes of 4i than that of
terminal alkene of VIII.
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OH
OH
Me
an easy approach to (E)-homoallylamine species with high
regio- and stereoselectivities. Further invDeOstIi:g1a0t.1io03n9s/Do0nGrCe0a0c1t9io6nA
mechanisms and applications are in progress in this laboratory.
View Article Online
Me
Me
SET
*
N
N
AYR
I
( )
AYR
Me
Me
2e
(
)
AYR
TsCl
Ts
Conflicts of interest
There are no conflicts to declare.
Cl-
OH
N
OH
N
*
2e
Me
2e
TsCl
II
( )
VI
(
)
(AYR = alizarin yellow R)
Ts
Ts
Acknowledgements
Me
Me
The authors are grateful for financial support from the National
Natural Science Foundation of China (No. 21762040 &
21762039). Ms. C.-Z. Shi and Ms. Q.-S. Xu contributed equally to
this work.
(less formed)
Me
Me
Ts
Ts
Ts
OH
OH
OH
N
N
N
III
(
)
Me
Me Me
Me
(IV)
VII
(
)
Calcd. 284.13149
Found. 284.13142
(not formed)
-HCHO
Notes and references
-HCHO
-HCHO
Me Me
N
Me
Me
Me
1
(a) K. Ouyang, W. Hao, W.-X. Zhang, Z. Xi, Chem. Rev., 2015,
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N
N
Ts
Me
Ts
Ts
V,
(
not detected)
4i
, main product)
(
VIII
( , minor product)
terminal alkene
2
(Z)-homoallylamine (E)-homoallylamine
3
4
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Scheme 3. Plausible pathway for the photocatalytic ring-opening sulfonylation of
N-methyl-4-piperidinol.
Experimental
To a 10 mL Schlenk tube equipped with a stir bar was added
sulfonyl chloride (1.0 equiv, 1.0 mmol), N-alkyl-4-piperidinol
(1.2 equiv, 1.2 mmol), alizarin yellow R (7 mg, 2 mol%), CaH2 (40
mg) and acetonitrile (2.0 mL). After stirred and irradiated with
white LED (30 W) under nitrogen for 24 hours at room
temperature, the reaction mixtures were quenched with
aqueous NHCl4 solution. 10 mL of ethyl acetate was added and
the organic layers were separated, washed with brine, dried
over anhydrous Na2SO4, and concentrated in reduced pressure
to afford crude homoallylamine product. The pure product was
obtained after silica gel chromatography using 5-10% ethyl
acetate/petroleum ether as the eluent.
5
6
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Conclusions
In summary, we have developed a novel, metal-free and direct
pathway for the ring-opening of N-alkyl-4-piperidinol through a
photo-catalyzed sulfonylation employing alizarin yellow R as the
organocatalyst. The reaction sequence involves an in situ
formed sulfonyl chloride/N-alkyl-4-piperidinol charge-transfer
complex that, under visible light irradiation and alizarin yellow
R catalysis, induced S-Cl bond cleavage of sulfonyl chloride. The
sulfonyl radical thus produced further reacted and induced both
the C-N and C-C bond cleavage of N-alkyl-4-piperidinols,
yielding the homoallylamine products. This protocol is
significantly green because it utilizes visible light as the greenest
reagent and a metal-free organic dye as the photocatalyst to
deliver the homoallylamine products at room temperature in a
simple one-pot procedure. Synthetically, this protocol provide
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This journal is © The Royal Society of Chemistry 20xx
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Green Chemistry
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Journal Name
ARTICLE
Reynolds, R. Angelaud, J. Girotti, A. Deese, C. Gu, L. Gazzard,
Org. Process Res. Dev., 2015, 19, 661.
View Article Online
DOI: 10.1039/D0GC00196A
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commercial sources and used as such.
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